I am planning a three-phase installation with Three Multiplus II 5kVA with a SMA Tripower 8kW on AC out. The system will run in ESS with backup functionality.
When taking the three-phase Victron training I found this statement, which was new to me:
"A three-phase system can not aid in phase balancing during charging. Each unit will always equally charge the battery"
This really worries me regarding backup or off-grid use. Could this prevent AC PV from being useful for charging the batteries, or even working at all? I assume that three phase PV inverters will try to deliver equal power to all phases, but what happens if one phase (e.g. L1) is heavily loaded and the others are not?
I would have assumed this scenario as an example:
- L1:Fully loaded, PV supplies 2 kW to load. Cannot charge battery.
- L2:No load, PV supplies 2kW to battery
- L3:No load, PV supplies 2kW to battery
But with the equal charge current rule it seems like the follwoing example is instead the case, where PV power cannot charge the battery during phase load imbalance:
- L1:Fully loaded, no power left to charge the battery
- L2:Cannot receive PV charge since L1 cannot charge
- L3:Cannot receive PV charge since L1 cannot charge
This would seem reasonable enough, but what worries me in this example is that it also seems to mean that the SMA inverter is then expected to deliver power to three very differently loaded phases. I am not certain that it has the specifications to handle that.
It seems to me that to make the backup/off-grid use case viable, either the PV inverter or the three phase Multiplus system will need to do some phase balancing!
Am I right? How does this work in real life? Is it possible at all?